Our industrial society has for many years used or proposed using sources and sinks of low grade thermal energy for a broad variety of purposes. For example, power plants, both nuclear and conventional, dissipate waste heat into rivers or other bodies of water. In that situation the river water which has a temperature in the same order of magnitude as the ambient environment acts as a sink of low grade thermal energy. In some industrial operations it is desirable to warm process streams, and fluids such as river water may be used as a source of low grade thermal energy. Ground water has been used for space heating or cooling; that is, as a source or sink of low grade thermal energy depending on its temperature relative to the surroundings. It has been proposed to use the low grade thermal energy in sewage to preheat air for space heating. It has been proposed to use domestic water as a sink of low grade thermal energy for cooling a refrigeration system. It takes little thought to recall scores of other applications of the low grade thermal energy exchange potential of fluids in the environment.
Heat exchange systems employing the low grade thermal energy potential of various fluids have been proposed or adopted without coordination, and ordinarily with little thought of the impact on other energy systems such as electrical utilities. To some extent this contributes to the electrical utilities' need for excess capacity to accommodate peak loads. It also results in somewhat ineffective utilization of the low grade thermal energy exchange potential of fluids that could desirably be used for heating and cooling.
The utilities that deliver domestic water have large quantities of liquid with excellent low grade thermal energy exchange potential flowing among the prospective users of such thermal energy exchange potential. One reason for not tapping this potential is the significant risk of hazard to public health and safety by uncontrolled access to a domestic water supply. It is, therefore, desirable to provide ways of effectively utilizing low grade thermal energy exchange potential already present in a community. It is desirable to employ low grade thermal energy exchange potential to alleviate usage of much higher grade energy such as electricity and fossil fuels.